Called every time a HTTP invocation is made. Simply allows the parent to setup the connection, and
then adds an Authorization HTTP header property that will be used for BASIC authentication.
The SecurityContextHolder is used to obtain the relevant principal and credentials.
Parameters: con - the HTTP connection to prepare Parameters: contentLength - the length of the content to send throws: IOException - if thrown by HttpURLConnection methods throws: AuthenticationCredentialsNotFoundException - if the SecurityContextHolder does not contain avalid Authentication with both its principal and credentials notnull |